Plasma Physics Reports最新文献

This work presents the results of a study on the selection of neutral beam injection system parameters for the projected Globus-3 spherical tokamak. The focus is on optimizing the energy and injection geometry to minimize fast particle losses and achieve efficient plasma heating. Two operating scenarios are considered: with low (1.5 T, 0.8 MA) and high (1.8 T, 2 MA) toroidal magnetic field and plasma current parameters. It is shown that the optimal injection energy range is 50–60 keV, which ensures a balance between minimizing shine-through losses and efficient heating of the plasma core. The study also analyzes the effect of the toroidal magnetic field ripple on the fast ion confinement. It is established that the thermal loads on the tokamak wall due to fast particle losses do not exceed critical values, even with non-ideal positioning of the first wall elements. The simulation results demonstrate that a neutral beam injection system with a power of up to 11.5 MW is capable of providing ion heating up to 20–40 keV, generating a non-inductive current of up to 700 kA and high plasma rotation, which opens up opportunities for research in the hot ion mode.

The results of studying plasma in the Globus-M2 spherical tokamak are presented in the scenario with injection of one neutral beam with energy of 46 keV and power of 0.925 MW in the stage of current ramp-up in the toroidal magnetic field of 0.95 T. In the experiment, the ion temperature as high as 4 keV, which had been reached previously only in the scenario involving sequential heating of plasma by two sources of high-energy atoms. The development of sawtooth oscillations leads to twofold decreases in the ion temperature and energy confinement time.

This article describes the results of an experimental study of the plasma ion component using the new CNPA-09 charge-exchange atom flux analyzer, part of the corpuscular diagnostics suite of the Globus-M2 spherical tokamak. The new instrument recorded charge-exchange atom spectra over a wide energy range—from thermal (0.8 keV) to above-injection (60 keV). Experiments with various heating methods were used to determine the plasma ion temperature from the thermal portion of the spectrum, and comparisons were made with data from other analyzers and spectroscopic diagnostics. Analysis of the high-energy portion of the spectrum provided information on the characteristics of fast particle deceleration, the influence of toroidal Alfvén eigenmodes on the confinement of suprathermal ions, and the behavior of particles with energies above the injection energy.

Accurate measurement of the spatial electron density distribution requires control of the relative alignment between the laser beam and collection optics in the Thomson scattering diagnostic. The most reliable way to monitor alignment is by detecting signals from two observation regions positioned above and below the laser beam axis. This is achieved with specially designed split-fiber bundles divided into two viewing areas. Detecting Thomson scattering light from both halves of the bundle with a filter polychromator enables online alignment monitoring and adjusting the system during the plasma experiment, simultaneously with plasma parameter measurements. Such an alignment system has been implemented in the Thomson scattering diagnostic on the Globus-M2 tokamak.

This work presents a review of corpuscular diagnostics methods used at the Globus-M2, TUMAN‑3M, and FT-2 plasma facilities at the Ioffe Institute. The results of recent experimental studies conducted at the Ioffe Institute are presented, illustrating the important role of corpuscular diagnostics in studying various aspects of the plasma behavior.

Results of measurements of electron temperature and density in the divertor region of the Globus-M2 tokamak near the lower X-point were obtained using helium imaging spectroscopy. The profiles of plasma parameters were compared with the measurement results of the Thomson scattering diagnostics and simulation results using the SOLPS-ITER code. The measurement and simulation results agreed satisfactorily despite a large spatial error of the measurement results of the helium imaging spectroscopy diagnostics. A correlation was discovered between the temperature and density profiles and the phase of the sawtooth oscillations of soft X-ray radiation.

The article analyzes the behavior of electron and ion components of Globus-M2 spherical tokamak plasma over a wide range of operating parameters (toroidal magnetic field up to 0.95 T and plasma current up to 0.45 MA) under its auxiliary heating by NBI-2 atomic beam with power up to 1 MW and particle energies up to 50 keV. From the device’s database, the authors selected more than 300 deuterium plasma discharges with deuterium beam injection meeting the criteria of data completeness, the condition for the formation of a quasi-stationary phase, and the absence of a locked MHD mode. Linear regression of data indicates strong dependence of electron thermal energy and electron temperature on the plasma current and moderate dependence on the toroidal magnetic field, while the influence of input beam power is negligible. Thermal insulation of ions in Globus-M2 tokamak plasma discharges is much better than thermal insulation of electrons, and energy confinement time is determined primarily by plasma’s electron component. Analysis of plasma stability in the gradient region showed that the development of electromagnetic instabilities is unlikely, while electrostatic electron temperature gradient mode is apparently unstable, and it determines electron heat transport.

A hot-ion mode has been achieved on the spherical tokamak Globus-M2 with both hydrogen and deuterium injection of high-energy neutral beams. Deuterium injection is shown to provide higher ion temperatures, toroidal rotation velocities, and thermal energy confinement times compared to those for hydrogen. Furthermore, ion thermal diffusivity is close to neoclassical level in case of deuterium injection, whereas for hydrogen injection it is significantly higher. The gyrokinetic simulation indicates that the toroidal rotation velocity gradient created by the deuterium beam can suppress the ion temperature gradient instability, thereby enabling the attainment of high ion temperatures. These results are important for understanding the mechanisms of energy confinement in spherical tokamaks.

The laser-induced quenching diagnostics of atomic hydrogen in the Globus-M2 tokamak divertor is described. The analysis is based on 2D distributions of plasma parameters simulated in SOLPS-ITER code for one of the discharges. Modeling of the expected background signals in spectral lines, as well as the working quenching signals, was performed using a collision-radiative model of deuterium atoms. A time-modulated thulium fiber laser working at 1875 nm with a peak power of 5 W was taken for the modeling as the laser source. The existing Thomson scattering divertor optical layout will be used for both laser probing and collection the fluorescence signal, allowing measurements to be performed in the Globus-M2 divertor inner leg.

Doppler backscattering (DBS) is a microwave diagnostics method typically used to study the poloidal plasma rotation velocity. It has become an integral part of plasma research on the largest tokamaks around the world. There are several DBS systems in use on the spherical Globus-M2 tokamak. The available probing frequencies provide measurements in a wide area spanning from the scrape-off layer (SOL) to half of the minor radius of the plasma. A multitude of results have been obtained using DBS after the upgrade on Globus-M2. These include research into the properties of magnetohydrodynamic (MHD). The phenomena of edge-localized modes (ELMs), tearing modes (TMs), Alfvén eigenmodes (AEs) and filaments were investigated.